I have a few questions due to some confusion. Appreciate a prompt guidance as always, please

A quick overview: My wife and children are on GTV dependent visa. I am on ILR and not on GTV. They are due to apply for ILR in Jan/25. Two of my children are 18.
- My wife can apply individually or she has to apply with her dependents? What about children over 18?
- What would be the form? SET M or O?
- I've heard that there is a different Fee for Appointment Services for SET M or O?
- I've also heard that the Standard Appointment Service is not available (for SET M or O) and one has to choose Priority or Super Priority?
- The fee for priority service will be for one application (main applicant and dependents) or separate for everyone? What about Children over 18?
- Applying individually is better for the cost or together. Please advise
Thanks
